The research will investigate several aspects of intravenous drug self-administration in baboons. One area of study will be the development and refinement of procedures for measuring the relative reinforcing efficacy of drugs. Procedures to be examined include: 1. fixed-ratio schedules with long time-out periods after each injection, 2. multiple fixed-interval schedules, and 3. discrete-trial choice procedures. Studies will involve both parametric manipulations and between drug comparisons. Systematic comparison of a series of anorectic stimulants will be undertaken, including d-amphetamine, diethylpropion, chlorphentermine, clortermine and mazindol. A second area of study will be an examination of pharmacological factors which interact with heroin and amphetamine reinforcement. These studies will employ both multiple fixed-interval schedules and choice procedures, and should provide information about mechanisms of drug reinforcement.